Perhaps the best policy against vote-stacking: 1. Run a checkuser on all accounts that ONLY participate in the AFD concerning the article. 2. If the checkuser is positive, block the user for sockpuppetteering for a week and leave note on talk page. 3. Block sockpuppets indefinitely.
This might deal with AFDs on 'fancruft' and other controversial matters... certainly worth a try!
Craig